1. Field of the Invention
This invention relates to automated vision inspection systems. In particular, this invention relates to integrated X-ray and visual inspection systems.
2. Description of Related Art
Automatic vision inspection systems have been used in many applications such as quality control, non destructive testing, and automatic manufacturing assembly processes. The design of such inspection systems depends on the nature of the applications. One important component of a vision inspection system is the sensing element which acquires the information about the object under inspection. Typical techniques of sensing include X-ray imaging, video camera, laser, etc.
X-ray imaging involves the use of an X-ray source that provides X-ray radiation through the object. The energy of the X-rays is attenuated in the penetration path. A sensing array, e.g. photo diodes, receives the attenuated X-rays and records the absorption profile. An image is created based on this absorption profile which reflects certain characteristics on the object under inspection. Automatic techniques in image analysis are then applied to process the image to detect any abnormal conditions.
Video camera imaging is another sensing technique that acquires the image of the object under inspection. In a system utilizing a video camera sensor, a video camera or optical imaging sensing array (e.g., charge coupled device array) is mounted at an appropriate location to view the object location. The image of the object in the visual frequency range is captured and digitized.
Each of the above techniques provides different types of information on the object under inspection depending on the specific application. One example of such an industrial inspection system is the inspection of electronic components on electronic assembly boards.
Inspecting electronic components on assembly boards involves the detection of assembly defects such as missing components, irregular solder paste, bad reflow, reverse polarity, wrong components, etc. Many new packaging technologies have presented challenges to automatic inspection. One example is Ball Grid Array (BGA) technology. Defects in BGA assemblies are difficult to detect. Some examples of BGA defects are: bridging, insufficient strength (too little solder), voids (due to contamination or paste problems), opens, poor wetting, solder balls (material ejected from solder during reflow), and misregistration (ball not centered on the pad).
In X-ray inspection, the X-rays penetrate through the connection and provide density information throughout the volume of the connection. Hidden defects can be easily detected by X-ray techniques. However, visual information may not be accurately obtained by X-rays. On the other hand, a video camera provides excellent visual information such as part labels, colors, etc. but cannot provide information on hidden structures such as solder joints under a chip carrier of a component with a BGA package.
Furthermore, traditional inspection is carried out on a fixed viewing basis. Although a fixed viewing inspection is simple, it does not provide complete information on the defects. For example, certain solder joints or lead defects can only be visible clearly at a certain orientation. Inspecting these areas at a fixed viewing angle may not reveal all the defects.
Accordingly, there is a need in the technology to provide a moving inspection and combine the two methods of inspection in an integrated environment to improve the inspection quality.